Improve code style, fix type errors

src/components/AnnouncementComponent.tsx

src/components/CourseListing.tsx

src/components/FilteredData.tsx

src/components/OMConfigComponent.tsx

src/components/PagingNavigation.tsx

src/components/Player.tsx

src/components/TypeEditor.tsx

src/misc/Util.tsx

src/pages/courses.tsx

src/pages/index.tsx